Over the years, a wide variety of boot liners and socks have been developed, some intended to be secured to the outer footwear, and some as separate from the footwear. One particular sock of the latter type is disclosed in U.S. Pat. No. 4,550,446. It comprises a sock made from a single piece of a fabric which is coated with a waterproof yet "breathable" layer of GORE-TEX (a trademark of the W. L. Gore & Associates, Inc.). A GORE-TEX coating is applied in the form of a membrane which is a microporous membrane of pure polytetraflourethylene (PTFE) containing more than nine billion pores per square inch. Each pore is twenty thousand times smaller than a drop of water, which makes the fabric to which it is laminated waterproof. Each pore is also, however, seven hundred times larger than a molecule of water vapor thereby allowing water vapor emitted from the foot to pass outwardly through the laminated fabric. This prior art sock may serve to keep the foot dry but it is essentially nonstretchable and difficulty is encountered in fitting it to various foot sizes without developing wrinkles and bunches, which detract from comfort and the uniformity of effect. Such a sock also is made of a relatively thin material and is not designed to be used to provide effective insulation against the cold.
Another sock or liner of which I am aware is a sock made out of a "stretch" material referred to as "STRETCH GORE-TEX". This material has the same characteristics from the standpoint of repelling transmission of water droplets while permitting "breathing" as the nonstretch laminate. The stretch sock is capable of being stretched to "form fit" the foot and ankle but it, like the first example given above, is not designed to provide insulation against the cold. It is also rather expensive to produce, since the entire sock is made of the "stretch" material.
I am also aware, of course, of thermal socks which are intended to insulate only, but do not contain the waterproof protection.
The principal object of my invention is to provide a sock which can be worn inside a wide variety of footwear and which is designed (a) to conform in shape to the contours of the foot, even though it includes a substantial quantity of nonstretch material; (b) which is designed to keep the foot dry, either by permitting escape of vapor from perspiration or from entry of outside water; and (c) which provides insulation against loss of warmth.
It is a further object of the invention to produce a sock which achieves the foregoing objectives and yet which can be manufactured and sold at a relatively reasonable cost, which is light in weight and which is capable of withstanding long and rugged use.